Third Party Review of Req/POs to Confirm Best Pricing

I’m hoping someone can provide some insight.  We have employees who want to purchase items or services.  We’re considering engaging a third party to review requisitions and/or purchase orders to ensure that we are getting the best pricing for these purchases.  Does anyone know of a good way to do this without any, or with minimal, customization if possible?  We would like to be able to track any changes made as a result of this third party review so that we can report on cost savings.  We're still on 11.5.10 so we don't want to spend a lot of time